Ceramic matrix composites (CMCs) have the capability to operate at temperatures up to 2400° F. (nearly 1320° C.) and future generations of CMCs protected by environmental barrier coatings offer the potential to withstand even higher operating temperatures. To decrease specific fuel consumption and reduce NOx emissions, CMC components based on composites of silicon carbide fibers in a silicon carbide matrix (SiC/SiC composites) are being developed for the hot sections of turbine engines. These CMC components include combustors, turbine shrouds, vanes and blades. A key enabling technology to support CMC component development is the ability to measure temperature and strain at temperatures of about 1320° C. and higher.
Thin-film metallic platinum-palladium (Pt/Pd) and ceramic indium oxide-indium tin oxide (InO/ITO) thermocouples have been tested under both thermal and mechanical cycling to determine their robustness. Although Pt:Pd and InO:ITO thin film thermocouples perform well in these cyclic tests, they have a relatively small thermoelectric power output for a given temperature. In addition, SiC/SiC composites produced by melt infiltration may have a significant percentage (e.g., about 2-10 vol. %) of free silicon due to incomplete conversion of molten silicon into silicon carbide; during high temperature exposure, this free or unreacted silicon may react with metals such as Pt in thermocouples.
To more accurately assess surface temperature and local temperature gradients on SiC/SiC CMC components, it would be advantageous to develop a new thermocouple approach that exhibits a significant improvement in thermoelectric power compared to Pt:Pd thin film thermocouples.